Sound reproducing apparatus



May 24, 1932. B. J. CHROMY SOUND REPRODUCING APPARATUS 2 Sheets-Sheet l Filed Oct. 15, 1928 INVENTOR.

ATTOR EY 2 Sheets-Shet 2 announcers.

D B n D 6 D E G D I3 I51 May 24, 1932.

Jr: sir-i I III, III'IIL BEN J. CHROMY, or .norxiNs, MINNESOTA,

Patented May 24,1932

ASSIGNOR T WIRED RADIO, 1N0, or miw I YORK, N; Y., A CORPORATION OF DELAWARE sonNn nnrnonnciNe APPARATUS Application filed October 15, 192 s. Serial No. 312,627. v Z

Thisinventi-on relates to sound reproductionin general and more specifically-to the reproduction of soundrecor'ded upon a" film strip. L

An object of this invention is to provide means whereby the sound record from a film strip may be reproduced without the use of lightrays.

- vide means whereby the sound'recordfrom a film strip may be reproduced without em p loying photo-electric devices. A in her object of this invention is to provide means whereby the sound record I from a film strip may be reproduced by causing the sound'record bearing portion of the film to vary the 'potential applied to an electrode of a thermionic vacuum tube.

" Other and further objects and features of this invention will be apparent to "those skilled in the art of sound reproduction from the following specification and the appended claims.

In this invention I provide novel means for reproducing sound records. The sound 7 record bearing-film strip is passed between two electrodes one of which is connected to anelectrode of a vacuum tube for varying the potential of that electrode withrespect to the other electrodes of the tube in accordance with the sound record of the film strip. The

electrodes between which the" film strip passes may be connected 'into several circuit ar rangements the preferred forms of which are illustrated in the accompanying drawings.

In the drawings Fig. 1 shows the electrodes between which the sou'nd'record passes connected I into a bridge circuit arrangement. Fig. 2 shows a modification of this invention.

' Fig. '3 shows another modification of this invention in which a four electrode thermionic vacuum tube is employed in the" reproduction of the sound record. Fig. 4 shows a further modification of this invention in which the sound record is employed to vary the magnitude of the radio frequency'volta'ge aap- Another object ofthis invention is to pro taken along the'line 6-6 of Fig. 7. Fig. 7 is a sectional viewof the electrodes taken along the 1ine'77' of Fig. 6.

Referring to Fig. 1 of the drawings in detail, 16-designates a vacuum tube detector having filament, grid and plate electrodes F, G and P respectively. A grid leak 17 is connected between the filament and grid electrodes. A bridgecircuit including variable resistances andvariable capacitiesis connected to the filament and grid electrodes of the vacuum tube 16. A sourceof high frequency current 1 is connected across the bridge circuit. Variablecapacities '2, 8 and 10 and variable resistances 3, 9 and 11 are connected inseries and make up three legs of the bridge circuit. 7 The capacity 2 andthe resistancefi form one leg of the bridge circuit; the ca-V pacity 8 and the resistance 9 form 'asecond leg of the bridge circuit; and the capacity IG and the resistance 11 form a third leg, of the bridgecircuit. Into the fourth leg of the bridge circuit are connected the electrodes 4, 4. These electrodes l, .4 are disposed upon the opposite sidesfiofthe sound record: bean ingportion of'the film;5.. a r

A source of electric current 12 is connected to r to the filamentof the audion 16., A source of 'anode potential 13- for the audion 16 is connected to the anode electrode of the audion 16 through the input circuitof the audio frequency amplifier 14.: A sound reproducing the grid will be substantially zero. When the balance in thebridge-circuit is disturbed, as for example, by varying either the resistance or the capacity of any of o the legs of'the bridge circuit, the source of high frequency currentsets up a potentialdifierence between the grid andfilament'electrodes of the tube 16. When the film strip 5 bearing'the sound record ismoved between the -electro'des4, .4 r

the balance of the bridge is'disturbed'in accordance with the sound record passingbetween the electrodes 4,4 and modulated high. frequency potential is impressed across the This modulated high frequency potential is filament and grid electrodes of the tube 16.

detected and modulated plate current is caused to flow in the plate circuit of the tube 16. This modulated plate current varies in accordance with the sound frequencies of the sound recorded upon the filmstrip 5., The

v modulated high'frequency potential may be to the filament of the audion 32. The output. circuit ofthe amplifierp34is;connected"tothe' 'outpu't of t'he tube 32." [A source of amplified in any conventional way before it isimpressed upon the input circuit of the detector tube 16.

' In Fig. 2 is illustrated a modified form of this invention. In this modification the gridfilament circuit of the vacuum tube or audion 32 is connected in series with the electrodes 24adjacent to the sound record bearing strip to the source of electrical oscillations 21. The capacity and resistance between-the elec-.

'trodes'24, 24 arevaried by the film strip 25.

Thevariable capacity 22 and variableresistance 23 and the variable capacity and variable resistance 29 are employed to con. trolthe amplitude of the electrical oscilla tions' derived from the source 21. The Variable resistance units 23 and 29 are shown connected in serieswith the, variable capacity units .22 and 30 respectively, however, these variable resistors may be connected in parallel with the variable capacity units.

source of high frequency21is connected across the bridge circuit. One terminal .of the 'source 21 is connectedto a point between 7 one of the electrodes 24and the variable ca-.

pacity22; the other. terminal'is connected to a ipointbetween the grid leak 28:.and the variable resistance 29. a

,1 A source of electric current 31 isconnected plate current 33 is-connected to the'plate electrode of the tube 32 through the input circuit of the amplifier 34. A sound reproducing'device is c'onnected to the output circuit of the'amplifier 34. Amplified electrical energy m'odulated in accordance with the sound 'record' carried by the .film 25 is fed to the sound reproducing device 35. e

When the film 25 is wound from'the reel 26 to the reel 27 it is causedto move between the" electrodes 24, 24. If the bridge circuit 22, 23, '24,24,G, F, 29, 30is balanced when clear film of a'certa'in'dimension is disposed between the electrodes 24, 24 then as the film 25 -bearing a sound record *is moved between the electrodes 24, 24 the bridge circuit-becomes unbalanced andfa diflerence of poten-. 'tial. is impressed across the grid and filament of the audion 32. "This potential-difference varies in accordance with the soundrecord on the film strip. A'current modulated in accordance with the sound record is caused to "flowin the anode'circuit ofjthe audion 32 andin the input circuit of the amplifier 34. The sound-reproducing device 35-is actu ated by the output of the amplifier and transi forms the electrical energy into sound Waves.

Another modification of this invention is shown in Fig. 3. In this modification a screen grid thermionic vacuum tube48 having filament or cathodeelectrodeF, grid electrode G, late electrode 1 andishielding' grid electrode is employed. A tuned circuit composed of the inductance 45 and the capacity 46 is connected to the'grid and filamentelectrodes of the vacuum tube. -A similar tuned circuit employing a capacity' 52 and an inductance 53 is connected to the anode and filament electrodes of the vacuum tube 48; A'source of anode current supply is connected between the jtuned circuit 52 53and the filamentelectrode F." A high frequency by-pass con filament F. The sound record bearingfilm V V 43 is moved between the electrodes 42, 42 as it is wound from reel 41 to'the reel44.

Sustained high frequency, oscillations are generated bythe interaction of the inputand' output circuits; of th'evacuum tube gf'when the tuned circiuts 45, 46 and 52,53 arein resonance to approximately the same frequency., Thesmall radio frequency current will oscillate" through the shielding gridcircuit -comprising the electrodes 42, 42 The film disposed between these electrodes acts as the dielectric. j

' The character of the sound: waves recorded upon the filnrstrip 43 varies the dielectric constant. 7 The radio frequency "oscillations in the shielding, grid circuit are,-- consequently modulated according tothe sound record on; the film 43. Correspondinglymodulated high frequency-potential is inducedacrossthe inductance 54 which is connected either to a high "frequency amplifier or to -.a detector tuber The film "43 maybe the ordinary celluloid filmsensitizedin the ordinary way and the sound record fixediupon it through the action ofpulsating light raysand the usual chemical. processes or .it maybe a strip-of waxy materialupon which indentations varying. in

depth or width in accordancewithwsound waves are'registered; Again the soundrec- 0rd maybe a strip'of mater-ial 'bearing perfo' rations which. vary in size and shape in accorda-nce with sound; waves. ;.Any. type of film in which the dielectric constant is varied in accordance withsou'nd waves-or, impulses may beu'sed in the sound reproducing devices ofithis invention.

Fig.4 shows a further modification of this invention. In this modification the output circuit of a high frequency oscillation generating vacuum tube 63 is coupled through the electrodes 70, 7 0,.between which a sound record bearing strip 69 is moved, to the input circuit of a vacuum tube 78. The output circuit of the vacuum tube 78 is coupled to an amplifier 79 which is connected to a sound reproducing device 80.

A tuned circuit comprising an inductance 61 and a capacity 62 is connected to the grip and filament electrodes of the vacuum tube 63. The filament of the audion 63 is excited by energy received from the source 64. The anode of the audion 63 is connected to the current source of supply 65. A. tuned circuit including an inductance 67 and a capacity 66 is connected between the plate and filament of the audion 63;

The frequency of the oscillations generated by the vacuum tube 63 is determined by the tuned circuits 61, 62 and 66, 67. This frequency should be rather high, preferably around 10,000 kilocycles to 20,000 kilocycles. At these high frequencies the transfer of high frequency energy through the capacity formed by the electrodes 70, is sufiicient to excite the input circuit of the audion 78 when a small vacuum tube having an output of five watts of high frequency ener y is employed as an oscillation generator 63.

A tuned circuit 7 3, 74 is connected to the grid and. filament electrodes of the audion 78. This circuit is tuned to resonance at the frequency of the oscillations generated by the vacuum tube 63. A grid leak 75 of high resistance and a small capaclty 76 are connected to the grid of the tube 78. A source of anode current supply 82is connected into the output circuit of the tube 78. The output circuit of the tube 78 is connected to the amplifier 79 which isconnected to the sound reproducing device 80. The sound record bearing strip 69 is wound upon either one of the reels 68 or 71. An electromagnetic and electrostatic shield 60 is provided for the oscillation generator 63 and its associated tuned circuits 61, 62 and 66, 67 A similar shield 7 2 is provided for the audion 78 and its associated amplifying circuits.

When the sound. record bearing film 69 is moved through the space between the electrodes 70, 7 0 the capacity and the radio frequency resistance between these electrodes is varied in accordance with the sound record. The magnitude of the radio frequency current transferred to the input circuit 7 8, 74 of the vacuum tube 78 is, therefore varied in accordance with the sound record. Electrical impulses, the wave form of which is governed by the sound record being reproduced from the film or strip 69 are rectified and amplified by the tube 78 and further amplified by the amplifier 79. A radio frequency, amplifier of any suitable type may be employed to amplify the electrical impulses ;before they are fed tector tube 78. r

In Fig. 5 is shown a film strip bearing a sound record in the. space 86 and pictures in the space-87. The spacecorresponding to to the circuits of the de the sound recording bearing space 86isthe part that is passed betweenthe electrodes 7 0,

70 ofFig. a, 4.2, 4.2 of Fig. 3, 24,24 of Fig.

Qandh'ofFig. 1'. T V I Figs. 6 and 7 illustrate the preferred form of the construction of the electrodes. Figs. 6 and 7.88 designates the sound record bea-ringlfiexible strip; 89 and: 90 designate an envelope ofinsulating material, suclioas quartz, glass or phenol. condensatlon products, surrounding the ribbonshaped metallic conductors'91 and 92 r Having thus described thepreferred forms high frequency oscillations, connectionsbetween said high frequency generating means and one of saldelectrodes,connections betweenthe other of saidelectrodes and the input circuit of said vacuum tube." v I 22in sound reproducing devices of the class described the combination of, a vacuum tube having input and out-put circuits, a sound record bearing strip, a source of high frequency oscillations a plurality of electrodes disposed adjacent to said sound record bearing strip, said electrodes and said film strip disposed adjacent to said electrodes comprising one leg of a bridge circuit arrangement, adjustable resistance elements disposed in the other legs of said bridge circuit, one of said electrodes being connected .to the input circuit of said vacuum tube, another of said electrodes being connected'to said source ing said strip between said electrodes for varying the transfer of high frequency energy trode connected to the input-circuit of' said of high frequency oscillations, means formovfrom said last named electrode to said elecvacuum tube in accordance with the sound record upon said strip.

3. In sound reproducing devices, the combination comprising, a source of high fre: quency oscillations, a vacuum tube having input and output circuits, a pair of electrodes, one of said electrodes being'connected to the input circuit of said vacuum tube and the other electrode being connected to said source of high frequency oscillations, said electrodes 4 v e v V 1,859,551

being connected into one arm of a Wheatstone bridgev circuit said Wheatstone bridge circuit including adjustableimpedance elements in each arm thereof, a dielectric hav g i'ng a dielectric constant greater than one disposed between said electrodes said dielectric having a sound record registered thereon, and means for moving said dielectric, the energy transferred from said source to said vacuum 1'6 tube input circuit being modulated in flCCOI'd-r anceivvith'said sound record. I V c 4. In a sound reproducingsystem, a .control circuit comprising an electron tube having input and output circuits, an amplifier system connected'with said output circuit, a

sound reproducer connected with said amplifier system, a Wheatstone bridge circuit ineluding variable resistance and capacity elements in three arms thereof and a variable 7 '20 capacity element in the remaining arm thereof, a source of high frequency currentrconnected across two :of the arms including said vari able capacity and resistance elements, and aconnection between the point of juncture of said la st mentionedzarms and said arm includingsaid-variable capacity, said variable capacity comprising asound film record operativebetween electrodes disposed'in the arm occupied byx-said variable condenser, said soundffilm record being movable to vary the capacity of said arm and correspondingly control the, effect of said high frequency current source upon the input circuit of said electron tube for controlling the operation ofsaid amplifier and correspondingly controlling the reproduction of sound. I 'Initestim'ony whereof I affix my signature. r r BEN J -CHR OMY. 

